This invention relates generally to a treatment for scoliosis and more specifically to the instruments, implants, distracting trial spacers, and surgical methodology used in the treatment and correction of scoliosis.
The bones and connective tissue of an adult human spinal column consists of more than 20 discrete bones. These more than 20 bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. They are coupled sequentially to one another by tri-joint complexes that consist of an anterior intervertebral disc and the two posterior facet joints. The anterior intervertebral discs of adjacent bones are cushioning cartilage spacers.
The spinal column of bones is highly complex in that it includes these 20 bones coupled to one another (and others), and it houses and protects critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complications, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.
Genetic, congenital and/or developmental irregularities are the principle causes that can result in spinal pathologies in which the natural curvature of the spine lost. Scoliosis is a very common one of these types of irregularities, resulting in a sequential misalignment of the bones and intervertebral discs of the spine. Major causes of scoliosis are idiopathic (i.e., unknown cause), congenital developmental anomalies and neuromuscular disorders such as cerebral palsy. The misalignment usually manifests itself in an asymmetry of the vertebral bodies, such that, over a sequence of spinal bones, the spine twists and/or bends to one side. In severe cases, neurological impairment and/or physiological disability may result.
The present surgical technique for treating scoliosis (as well as other spinal conditions) includes the implantation of a plurality of hooks and/or screws into the spinal bones, connecting rods to these elements, physically bracing the bones into the desired positions, and permitting the bones to fuse across the entire assembly. This immobilization often requires anterior plates, rods and screws and posterior rods, hooks and/or screws. Alternatively, spacer elements are positioned between the sequential bones, which spacers are often designed to permit fusion of the bone into the matrix of the spacer from either end, hastening the necessary rigidity of the developing bone structure. Spacers allow bone fusion to grow into or around them. There are two classes of intervertebral spacers: horizontal cages such as the BAK(trademark) and Ray cages, as described and set forth in exemplary U.S. Pat. Nos. 5,015,247 to Michelson and 5,026,373 to Ray et al., respectively, and vertical cages such the Harms cages, as described and set forth in exemplary U.S. Pat. No. 4,820,305.
Similar techniques have been employed in other spinal infirmities, including collapsed disc spaces (failure of the intervertebral disc), traumatic fractures, and other degenerative disorders. While the present invention has many applications, such applications include the treatment of any spinal disorder in which the space between vertebral bones needs to be surgically separated (the bones distracted), realigned and then fused to one another.
A variety of systems have been disclosed in the art which achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back that needs to be immobilized, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. With respect to the failure of the intervertebral disc, and the insertion of implants and/or height restorative devices, several methods and devices have been disclosed in the prior art.
Restoring the appropriate height and orientation of the vertebral bones and the intervertebral space is the first step in the surgical strategy for correcting this condition. Once this is achieved, one class of surgical implantation procedures involves positioning a device into the intervening space. This may be done through a posterior approach, a lateral approach, or an anterior approach. Various implant devices for this purpose include femoral ring allograft, cylindrical metallic devices (i.e., cages), and metal mesh structures that may be filled with suitable bone graft materials. Some of these implant devices are only suitable for one direction of approach to the spine. All of these devices, however, are provided with the intention that the adjacent bones will, once restored to their appropriate alignment and separation, then grow together across the space and fuse together (or at least fuse into the device implanted between the bones).
Most recently, the development of non-fusion implant devices, which purport to permit continued natural movement in the tri-joint complex have provided great promise. The instrumentation and methods for the implantation of these non-fusion devices, as well as the implantation of the fusion devices catalogued previously, therefore should integrate the functions of restoring proper anatomical spacing and easy insertion of the selected device into the formed volume.
It is, therefore, an object of the present invention to provide a new and novel treatment for scoliosis, as well as for the treatment of spinal pathologies in general.
It is, correspondingly, another object of the present invention to provide an intervertebral distraction trial tool which more accurately and easily separates collapsed intervertebral spaces.
It is further an object of the present invention to provide an intervertebral distraction trial tool which more can be used to correct scoliosis and/or restore normal alignment to the spine.
It is further an object of the present invention to provide an instrument that proficiently and simply manages the insertion, rotation, and removal of the intervertebral distraction trial tools.
It is further an object of the present invention to provide an implantable spacer device that permits more anatomically appropriate and rapidly osteogenic fusion across the intervertebral space.
Other objects of the present invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.
The present invention is directed to a method of treatment of scoliosis and other spinal disorders. This method of treatment further includes several new and novel instruments, implantable trial distraction elements, and intervertebral spacer implants. Inasmuch as the description of the new and novel method cannot be complete without a description of each of these integral members, the following includes ample explanation of these elements as well as description of the surgical techniques.
First, the patient spine is exposed through an anterior approach (i.e., the surgeon creates an access hole which permits direct interaction with the anterior and/or anterior-lateral portion of the intervertebral bodies). In the case of scoliosis, as well as in other disorders in which the intervertebral space requires distraction and/or repositioning, the surgeon removes the intervertebral disc material, usually leaving some portion of the annulus (the cylindrical weave of fibrous tissue which normally surrounds and constrains the softer cartilage cushion of the disc material). The surgeon then, in succession, inserts a series of intervertebral trial spacers of defined width. Each of the series of spacers is of a progressively wider thickness, resulting in the continual widening of the space until restoration of the proper disc height has been achieved. Proper disc height restoration is determined by surgical experience, and by observation of the annulus. (Often, the tightening of the annulus indicates that the proper disc height has been reached, inasmuch as the annulus is much less likely to be distorted by the same disruption that caused the intervertebral disc to collapse in the first place.)
More particularly, with respect to the specific instruments disclosed herein, a series of solid trial spacer elements and an instrument for their insertion and removal is now provided. Each trial spacer is a generally cylindrical disc having a deep annular groove at its midpoint, which forms a central trunk and radial flanges at each end of the trunk. Stated alternatively, two cylindrical upper and lower halves of the disc are held in a closely coaxial spaced apart association by the central trunk, which forms a coaxial bridge between the upper and lower halves. The annular groove is particularly useful for holding the spacer using the spacer insertion instrument of the invention, described below, in that the holding end of the insertion instrument fits within the groove.
A variety of features of embodiments of the trial spacer elements are disclosed. In some embodiments, such as the first and second embodiments described below, support portions (the portions that are in contact with the adjacent vertebral bodies when the spacer is disposed between the bodies) of the top and bottom surfaces are parallel. Spacers having this feature are generally described herein as xe2x80x9cconstant thicknessxe2x80x9d trial spacers. In other embodiments, such as the third and fourth embodiments described below, the support portions are not parallel, providing an overall taper to the spacer at an angle. Spacers having this feature are generally described herein as xe2x80x9ctapered thicknessxe2x80x9d trial spacers. The tapered thickness trial spacers are particularly useful for treating scoliosis, as described below.
Other features of embodiments of the trial spacer elements include beveled flanges and non-parallel annular groove walls. More specifically, in some embodiments, such as the second and fourth embodiments described below, the flanges are radially beveled in that an outer edge of the top surface of the disc is tapered toward an outer edge of the bottom surface of the disc. In other embodiments, such as the first and third embodiments described below, the flanges are not radially beveled in this manner. The radial beveling feature can be particularly useful for easing the insertion of the spacer in between collapsed vertebral bodies, as described below. Further, in some embodiments, such as the first and third embodiments described below, the walls of the annular groove are parallel, such that the floor of the groove is as wide as the opening of the groove. In other embodiments, such as the second and fourth embodiments described below, the walls of the annular groove are tapered toward one another with the increasing depth of the groove, such that the floor of the groove is narrower than the opening of the groove. Each type of annular groove is useful, depending on the particular surgical application and on the particular embodiment of the spacer insertion instrument that is used to insert the spacer.
Collections of trial spacer elements are provided by the invention. Preferably, each spacer in a particular set maintains the same diameter as the other spacers in the set. (It shall be understood that different collections of spacers may be provided such that the diameter of the selected collection of trial spacers is appropriate for the specific patient being treated.) Also preferably, each spacer in a particular set has a predetermined depth that differs from the depth of the other spacers in the set. The predetermined depth is provided in that while each spacer in the set shares the same annular groove dimensions (so that each can be held by the same insertion instrument), each spacer has a different flange thickness (in sets where the spacers are constant thickness spacers). For sets of tapered thickness spacers, the predetermined maximum depth and predetermined minimum depth (the two depths providing the overall taper) are provided in that while each spacer in the set shares the same annular groove dimensions (so that each can be held by the same insertion instrument), each spacer has a different maximum flange thickness and a different minimum flange thickness. Preferably in sets of tapered thickness spacers, the overall taper angle is the same for each spacer in the set. The usefulness of providing sets of spacers similar in most respects except for the depth dimension will be described in greater detail below.
With regard to the instrument for the insertion and removal of the trial spacer elements, a first embodiment (particularly useful for inserting constant thickness trial spacers) of a spacer insertion tool includes an elongated shaft and a handle at one end of the shaft. The distal end of the shaft includes semi-circular hook that is adapted to hold a trial spacer within an enclosure formed by the hook. The angle swept out by the hook is slightly greater than 180 degrees, but the inner diameter of the hook is only slightly larger than the central trunk of the trial spacer. Therfore, the trial spacer may be snapped into the enclosure, but maintains complete rational freedom within its grasp. A loading tool may be provided to assist in the loading and unloading of the trial spacer from the trial spacer insertion instrument of this embodiment. This loading tool comprises a forked hook having two curved tines separated by a notch that engages the shaft of the insertion tool as the tines engage the flanges of the trial spacer, to force the trial spacer into the enclosure. Alternatively and/or additionally, the same device may be utilized to remove the spacer from the enclosure, by reversing the position of the forked hook relative to the insertion tool and the spacer.
The section tool of this embodiment can be used to insert a series of constant thickness trial spacers (some of which may have beveled flange edges for easing the insertion between the collapsed bones and into the space to be distracted). More specifically, thinner trial spacers can initially be inserted into the spacer, followed successively by thicker trial spacers until the desired spacing is achieved. Once the appropriate spacing has been achieved, immobilization of the spine by fixation, fusion, or non-fusion techniques and devices, such as those set forth in co-pending U.S. patent application Ser. Nos. 09/906,117 and 09/906,118, entitled xe2x80x9cAn Intervertebral Spacer Device Having a Wave Washer Force Restoring Elementxe2x80x9d and xe2x80x9cAn Intervertebral Spacer Device Having a Spiral Wave Washer Force Restoring Elementxe2x80x9d, respectively, as well as U.S. Pat. No. 5,989,291, entitled xe2x80x9cAn Intervertebral Spacer Devicexe2x80x9d, each of which has been assigned to the same assignee as this present invention, the specifications of which are all fully incorporated herein by reference, may be desirable.
While simple distraction to a constant height across the intervertebral space is appropriate for standard disc compression pathologies, in the case of scoliosis, simple constant thickness distraction is insufficient to remediate the pathological condition. What is necessary is the distraction of the sequence of spaces, each to an appropriate angle and height, such that the overall spinal configuration is anatomically correct. Tapered trial spacers, such as those disclosed in the present application, are the first such distraction tools to provide such a tailored correction of the misangulation of the spinal bones.
More particularly, the surgeon inserts the tapered trial spacers into the intervertebral space (presumably from the anterior, or anterio-lateral, approach) with the narrow edge of the trial spacer forming a wedge and sliding between the adjacent bones. By utilizing either a second or third embodiment of the spacer insertion tool, described more fully below, the surgeon may turn the spacer around its axis within the intervertebral space to find the most appropriate rotational position (corresponding to the most desirable straightening effect on the spinal column). Stated alternatively, each of the tapered trial spacers has an overall wedge shape that generally corresponds to the pathological tapering of the adjacent bones that characterizes scoliosis. By rotating the wedge-shaped spacer after it has been placed between the adjacent bones, the overall disc alignment may be compensated, restoring appropriate anatomical status. It should be understood that additional rotation of the spacer may restore lordosis to the spine, and that over-rotation (if the particular spine is flexible enough) of the spacer would result in a pathological curvature in the opposite direction.
This second embodiment of the spacer insertion tool includes a handle and an elongated dual shaft, the dual shaft culminating in a trial spacer grasping pincer, rather than the simple hook of the first embodiment. This pincer differs from the hook of the first embodiment of the trial spacer insertion tool described above, inasmuch as the dual shaft includes a fixed shaft and a selectively engagable shaft which, together, form pincer. More specifically, the fixed shaft includes a semicircular hook portion of the pincer at its distal end, having an enclosure within which a trial spacer can be placed. The selectively engagable shaft includes the complementary portion of the pincer, which moves toward the hook portion to grasp and hold the trial spacer when the engagable shaft is engaged, and moves away from the hook portion to release the trial spacer when the engagable shaft is disengaged. (The spacer can be unloaded and loaded when the engagable shaft is disengaged.) The engagement action prevents the spacer from moving relative to the tool, and therefore permits the surgeon to rotate the tapered spacer in between the vertebral bodies (by contrast, the first embodiment of the trial spacer insertion instrument permitted the spacer to rotate freely in the enclosure of the hook). There are alternative insertion and rotating instruments that may be designed, so long as they selectively and alternatingly release or hold the trial spacer securely against rotation (the spacer cannot be permitted to rotate freely if it must be turned in the intervertebral space). The tapered trial spacers themselves can include angle markers that clearly indicate to the surgeon the amount of rotation that was necessary for the correction of the spinal deformity. Such angle markers can also serve as a guide for the implantation of a secondary bone graft (e.g., a femoral ring) or another intervertebral spacer device.
Once the surgeon has determined the appropriate geometry for the surgical implants via the trial spacers, he or she is ready to immobilize the spine in that position. While multiple ways for immobilizing the spine are disclosed in the prior art, any one of which and others may be suitable for the specific surgical patient""s treatment, three alternative ways are herein described.
First, the trial spacers may be left in the patient while rod fixation apparatuses (anterior or posterior) are mounted to the spine, thereby holding the spine in its desired orientation even after the trial spacers are subsequently removed. Alternatively, surface plating and/or intervertebral cage devices may be mounted to the spine to promote fusion without the need for bulky rod assemblies. (While this approach may seem more surgically desirable, questions regarding the long term stability of these constructs have led some surgeons to chose combinations of rodding and cages.)
A third approach to immobilizing the corrected spine is to insert a shaped bone graft, or suitably contoured porous metal spacer, into the properly distracted intervertebral space, and either plating or using rod fixation to hold the construct stable as the spine fuses. The insertion of a femoral ring allograft, or porous metal implant, into an intervertebral space is described more fully in co-pending U.S. patent application Ser. Nos. 09/844,904 and 09/906,123, respectively entitled xe2x80x9cA Porous Interbody Fusion Device Having Integrated Polyaxial Locking Interference Screwsxe2x80x9d and xe2x80x9cPorous Intervertebral Distraction Spacersxe2x80x9d, assigned to the same assignee as the present invention, the specifications of each being fully incorporated herein by reference.
The tapered trial spacers may also serve as precursors (measuring instruments) for another spacer (e.g., a porous metal spacer), similarly shaped, which is inserted into the intervertebral space by the same instrument.
Therefore, the present invention, in its many embodiments and components, is directed to a surgical treatment for restoring a proper anatomical spacing and alignment to vertebral bones of a scoliosis patient. In one desired embodiment, the present invention comprises a surgical method, which in a first embodiment, comprises: 1. determining an angular misalignment associated with at least one pair of adjacent vertebral bones; 2. sequentially inserting and removing a series of progressively wider cylindrical spacer elements into the corresponding intervertebral space between said at least one pair of adjacent vertebral bones until the proper anatomical spacing between the pair of adjacent vertebral bones is restored; 3. for each intervertebral space, inserting a diametrically tapered cylindrical spacer element into the intervertebral space between said corresponding pair of adjacent vertebral bones; and 4. rotating said diametrically tapered cylindrical spacer element such that the rotational orientation of the tapered cylindrical spacer element introduces the appropriate counter offset to the intervertebral space of the previously misaligned scoliotic vertebral bones, thereby restoring the proper anatomical alignment of the vertebral bones.
It shall be understood that each of said progressively wider cylindrical spacer elements includes substantially parallel upper and lower surfaces. The method may also include the additional step of affixing immobilizing instrumentation to the vertebral bones of the patient to hold the restored vertebral bones rigidly in position to facilitate fusion, and positioning bone fusion material adjacent to the restored vertebral bones. It shall be understood that other equivalent (or alternatively efficacious) means for facilitating healing, such as including positioning a non-fusion intervertebral spacer device between the restored vertebral bones so that a proper anatomical motion may be possible.
The surgical treatment set forth above should be further refined inasmuch with respect to the diametrically tapered cylindrical spacer elements, such that each has a width along its central cylindrical axis substantially equivalent to the axial width of the final cylindrical spacer element utilized in the step of sequentially inserting and removing the series of progressively wider cylindrical spacer elements to restore the proper anatomical spacing between the pair of adjacent vertebral bones.
It shall be understood that each progressively wider cylindrical spacer element and/or diametrically tapered cylindrical spacer element may comprise solid or porous metal, or a porous or non-porous organic implantable material.
For clarity, this embodiment of the surgical method includes exposing an intervertebral space between adjacent vertebral bones, distracting the space by sequentially inserting therein and subsequently removing therefrom a plurality of intervertebral spacers, each having a predetermined thickness, the thicknesses incrementally increasing from one spacer to another at an increment acceptable for safely distracting the space to a desired distance, and when adjustment of an angular misalignment of the adjacent vertebral bones is necessary, inserting, and when necessary rotating, in the intervertebral space, at least one diametrically tapered intervertebral spacer having a thickness along its central cylindrical axis sufficient to maintain the desired distance between the adjacent vertebral bones, and a diametrical angle sufficient to reorient the adjacent bones to the desired configuration, when rotational adjustment of the angular misalignment is necessary, rotating said tapered intervertebral spacer within the space until the desired alignment is established.
In an alternative embodiment, in which porous spacers are utilized, the surgical method of the present invention may comprise: determining an angular misalignment associated with at least one pair of adjacent vertebral bones; sequentially inserting and removing a series of progressively wider cylindrical spacer elements into the corresponding intervertebral space between said at least one pair of adjacent vertebral bones until the proper anatomical spacing between the pair of adjacent vertebral bones is restored; for each intervertebral space, inserting a diametrically tapered cylindrical porous spacer element into the intervertebral space between said corresponding pair of adjacent vertebral bones; rotating said diametrically tapered cylindrical porous spacer element such that the rotational orientation of the tapered cylindrical porous spacer element introduces the appropriate counter offset to the intervertebral space of the previously misaligned scoliotic vertebral bones, thereby restoring the proper anatomical alignment of the vertebral bones; and stabilizing the pair of adjacent vertebral bones to permit infused growth of bone into the diametrically tapered cylindrical porous spacer element.
As shall be readily understood, in its most basic form, the method of the present invention principally consists of sequentially inserting and removing a series of progressively wider cylindrical spacer elements into the intervertebral space between adjacent vertebral bones until the distance between the vertebral bones is anatomically appropriate.
More particularly, with respect to the various spacers of the present invention, in its most basic form, the spacers comprise a plurality of sequentially axially wider disc spacer elements, the sequential insertion and removal of which, into an intervertebral space effects a widening of the intervertebral space, such that a desired anatomical spacing of adjacent vertebral bones may be restored. These spacers may include beveled upper and lower circumferential radial edges which facilitate the application of the desired spreading force to the adjacent vertebral bones. For the ease of surgical use, these spacers may each include an engagement locus which couples with a corresponding insertion and removal tool to facilitate the same. This locus comprises an axially medial groove into which said insertion and removal tool can be seated. In two alternative embodiments, the medial groove may comprises a constant width, such that each disc spacer element may rotate freely within the corresponding insertion and removal tool. Alternatively, the groove may be a radially widening groove, such that each disc spacer element may be prevented from rotating freely with respect to the corresponding insertion and removal tool by a clamping action thereof, thereby permitting the controlled rotation of the corresponding disc spacer element within the intervertebral space by manipulation of the insertion and removal tool.
Tapered spacers, for use in reorienting as well as distracting the alignment of the adjacent vertebral bones may be used. These tapered spacers comprise diametrically tapered upper and lower surfaces. Ideally, for surgeon measurement purposes, each of the disc spacer elements includes at least two relative angle designation marks on at least one of said upper and lower surfaces such that a surgeon user may readily visually determine the rotational angle of said disc spacer element relative to a known reference.
It shall be understood that the intervertebral spacers each have a unique axial thickness, the thicknesses increasing sequentially from one spacer to another, the increasing thicknesses increasing incrementally, said plurality of spacers being particularly useful for gradually distracting adjacent vertebral bones in an anatomically appropriate manner.
A critical feature of the present invention is the potential for using porous spacers to distract and potentially reorient the spine, and that the spacers may be implanted permanently into the space between the vertebral bones such that bone ingrowth and solid fusion may occur across the intervertebral space.
As introduced above, insertion tools are additional components of the present invention. In a first embodiment, the instrument for inserting and removing an intervertebral spacer into and out from an intervertebral space between adjacent vertebral bones, the spacer having a trunk portion having a longitudinal axis and flange portions at each longitudinal end of the trunk, the instrument comprises: a shaft having a proximal end and a distal end; said proximal end including a handle; and a holding structure provided at the distal end, which holding structure includes an enclosure within which the trunk of the spacer may be selectively introduced and maintained therein, the holding structure having an opening leading to the enclosure and through which opening the trunk of the spacer may be selectively passed to when forced therethough. More specifically, the trunk of the spacer has a first width, the opening has a second width which is incrementally smaller than the first width, and the enclosure has a third width which accommodates the first width, such that selective introduction of the trunk through the opening and into the enclosure requires a force to elastically widen the opening such that the trunk may pass through the opening and into the enclosure, the restoration of the opening providing an occlusion which maintains the trunk within the enclosure. As suggested above, the trunk is generally cylindrical and, therefore, the holding structure includes a hook having a curvate extent which forms a partial-circular enclosure, and which curvate extent fits between the flanges when the trunk is maintained within the enclosure.
In such an embodiment, the intervertebral spacer is selectively snapped into and out of the enclosure through the opening, and such that the intervertebral spacer may be rotationally freely held within the enclosure. In order to snap the spacer into and out of the enclosure, a second element is often utilized. This second helper tool comprises a handle portion at one end, and a bifurcated pair of spaced apart curvate hook-shaped times at the other. The times have a radius of curvature greater than that of each of the spacers, such that when the first and second elements engage one another (at a fulcrum point at the point of bifurcation of the spaced apart curvate hook-shaped tines and a point between the handle and enclosure ends of the first element), the introduction and removal of the distraction member from the enclosure is facilitated.
In a second embodiment, which is more suited for the insertion, rotation and removal of the tapered spacers, the tool comprises a shaft having a proximal end and a distal end, said proximal end forming a handle and the distal end forming a spacer member engaging subassembly; said spacer member engaging subassembly including at least one selectively expanding and contracting enclosure into which the central core may be introduced when the engaging subassembly is in the expanded state, and which holds the spacer member so that it cannot move when the selectively expanding and contracting enclosure is rendered into the contracted state; and an actuating mechanism, extending from the proximal end to the distal end, by which the spacer member engaging subassembly may be selectively expanded and contracted. More specifically, the spacer member engaging subassembly comprises a fixed curvate hook defining a portion of the enclosure, a second, selectively advanceable and retractable, portion adjacent the fixed hook portion and said first and second portions forming said selectively expanding and contracting enclosure. Stated alternatively, the selectively expanding and contracting enclosure is formed by at least two members which are maintained in selectively slideable association with each other, at least one of said at least two members including a tapered edge thereof.
The instrument of this embodiment includes an actuating mechanism including a trigger element disposed in the handle portion, which trigger is actionably coupled to advancing and retracting cams which are coupled to the second portion to advance and retract the second portion in accordance with selective manipulation of the trigger. In more detail, the spacer member engaging subassembly comprises a fixed member and a selectively moveable member which, together, form said selectively expanding and contracting enclosure, and wherein said actuating mechanism comprises a trigger which is mechanically coupled to said selectively moveable member, the mechanical coupling including a rod, a plate having a protrusion, and a lever having a slot, the rod being connected at one end to the selectively moveable member and at another end to the plate, the protrusion engaging the slot, the lever being attached to the trigger, so that when the trigger is engaged, the lever pulls the plate protrusion by the slot, the plate pulls the rod, and the rod moves the selectively moveable member toward the fixed member.
In a third embodiment, the tool comprises a shaft having a proximal end forming a handle, and a distal end forming a claw subassembly for holding said spacer, said claw subassembly including a first pincer which is fixed at the distal end of the shaft and a second pincer which is selectively rotateable into and out of spacer holding association with said first pincer to hold and release, respectively, the spacer; and an actuation mechanism for selectively rotating the second pincer. The second pincer is rotateably mounted to the shaft and is spring biased away from the first pincer.
In this embodiment the actuation mechanism comprises a sliding member mounted to a the shaft which is selectively moveable in the distal direction by a force sufficient to overcome the bias of the spring, the distally directed movement of the sliding member thereby causing the second pincer to move toward the fixed first pincer, and the subsequent retraction of the sliding member in a proximal direction causes the sliding member to disengage the second pincer and the permits the pincers to separate under the bias of the spring. In order to facilitate this action, the second pincer includes a tapered surface which is engaged by a corresponding surface of the sliding member, said engagement causes the second pincer to rotate relative to the first pincer.
More specifically, the intervertebral spacer comprises a cylindrical member having an annular groove defining a central axial core portion and a pair of flange portions at opposing ends thereof; and the claw subassembly engages the spacer at the central axial core.
Stated alternatively, this third embodiment comprises a pair of pincers, a first of this pair being fixed, and a second being coupled to the first in open-biased opposition thereto, and a sliding element which may be selectively translated into and out of engagement with said second pincer to close and open the pair of pincers, respectively. The pair of pincers define an intervertebral spacer grasping enclosure having an access opening through which the intervertebral spacer can be passed for placement into the enclosure when the sliding element is out of engagement with the second pincer, and the spacer is securely maintained between the first and second pincers when the sliding element has been translated into engagement with the second pincer. Ideally, the first and second pincers are mounted at the distal end of a common shaft, and the sliding element is translateable along said shaft; and wherein the second pincer has a portion thereof which is engaged by the sliding element to close the pair of pincers. In addition, the second pincer is mounted to the common shaft by a pivot joint, and the portion of the second pincer which is engaged by the sliding element is a tapered surface, the angle of which tapered surface, when engaged by the sliding element, causes the second pincer to rotate about the pivot joint, closing the first and second pincers.